The invention relates to a process and device for extinguishing metal fires by application of an extinguishing agent to the fire source.
Metal fires, namely fires of the fire class D (Magnesium alloys, aluminum alloys, lithium alloys, sodium, etc.) pose a serious problem in fire fighting. The reason for this lies in the strong reaction of these metals (in particular alkali metals) with even minute quantities of water. Even a high relative humidity of the surrounding air is sufficient to accelerate the combustion process.
Metals involved in metal fires are particularly the alkali metals sodium, potassium, lithium, and cesium, the metals magnesium, calcium and barium which also react violently with water, and the metals aluminum, cerium, iridium, niobium, palladium and also magnesium oxide.
Due to the increased technical use of such metal alloys, for example in the automotive sector, the problem of fire fighting has been considerably amplified as even chippings which occur during metal-removing shaping of components of such alloys constitute a considerable fire risk. Car manufacturers worldwide are currently working on the increased use of magnesium components in vehicles, for example, in engines, gear-boxes, axles, doors, etc. The result is that in traffic accidents with such vehicles today and in particular in the future, there is an increased risk of fire with the major problem that, at present, the emergency forces cannot fight such fires in a targeted manner. The fire fighting services have presently no suitable extinguishing agents for effective action against fires of this type.
The combustion temperatures of the above metal alloys lie far above 2000° C. On contact with water this leads to dissociation of the water molecules, which are split into hydrogen and oxygen. This splitting can lead to gas explosions, which constitutes an additional potential risk.
Fighting metal fires with the extinguishing agents, which are known today, does not involve a true extinguishing process but merely the covering of a fire source, because of the nature of the extinguishing agents used until now. Extinguishing agents used at present are salt (sodium chloride—potassium chloride), extinguishing powder fire class D, sand and grey cast iron chippings. These can only be used to cover the burning metal. No extinguishing process as such is possible at present with any of these agents. If the burning metal is however merely covered by the extinguishing agent, the fire extinguishing process can take several hours or even days. This is an unacceptable situation for metal workers.
The use of the extinguishing powders which are known so far has the further disadvantage that pollution of the production plant occurs to a very high degree if a fire must be extinguished in the area of the plant. This calls for time-consuming and expensive clean-up work and hence long downtimes of the costly production equipment. Furthermore, the dust formation from fire fighting with powder results in a corresponding health risk for the fire fighters, as the fine powder dust remains in the lungs after inhalation and cannot be removed.
Grey cast iron chippings as a covering agent for metal fires also have considerable inadequacies in handling. Major German car manufacturers keep large quantities of grey cast iron chippings for any metal fires. A considerable problem connected with grey cast iron chippings however is the occurrence of corrosion by air oxygen. When these rusty chips are applied for example to burning magnesium chippings, this in turn lead can to undesirable reactions. These reactions are attributable to the iron oxide (rust has the chemical formula FeO(OH)). When heated to a high temperature, water is released and this water from the iron oxide in turn leads to corresponding reactions with the magnesium.
A similar problem arises with sand as an extinguishing agent, which therefore must be stored under absolutely dry conditions. Damp sand leads to the same phenomena as oxidized grey cast iron chippings.
It is therefore the object of the present invention to provide a process and a device for extinguishing metal fires with which the problems indicated can be avoided at least to a considerable extent.